ON THE PLANT REMAINS IN THE SCOTTISH PEAT MOSSES. 65 



The observations from the Shetlands illustrate the same feature, for although the 

 Second Arctic Bed is present, yet the Upper Forest does not seem to have spread over 

 the peat areas. Shortly stated, the farther one passes to the edge of the Continental 

 plateau the more uniform does the flora appear to have remained since the later stages 

 of the glacial period. This may imply either that the climatic conditions have been 

 more uniform in those regions, or that the successive waves of vegetation passing over 

 the mainland did not penetrate there on account of natural barriers to immigration. 

 The peat does not afford any direct evidence upon these points, for whilst the Second 

 Arctic Bed was being formed on the mainland, the peat mosses of the Hebrides were 

 covered with marsh consisting of Phragmites communis and Equisetum, which might 

 well occur under cold or under temperate conditions. 



The Upper Peat Bog is developed in all districts, and the flora is generally very 

 similar to that of the Lower Peat Bog. In some of the Highland areas, such as the 

 Spey-Findhorn watershed, Findhorn-Nairn watershed, Coire Bog, Cape Wrath district, 

 Rannoch Muir, remains of small Betula alba shrubs occur in the lower parts of this zone. 

 The wood is very local in occurrence, whilst the main mass of the peat is formed 

 of Scirpus csespitosus, Eriophorum angustifolium, E. vaginatum, and Sphagnum. 

 Evidently these small clumps of shrubby birch were soon displaced, as no wood is met 

 with above the first foot or so of the Upper Peat Bog. In the Hebrides and the 

 lowland mosses of Wigtownshire the Upper Peat Bog is simply a continuation of the 

 Lower Peat Bog, there being no layer of arctic plants between. 



The Upper Forest Bed. — This zone is confined to the mainland of Scotland from 

 the lowland mosses of Wigtownshire to the valley of the Dionard, south of the Kyle 

 of Durness. Whilst the flora exhibits remarkable uniformity, some interesting and 

 important modifications appear as the bed is traced northwards through Scotland. In 

 the areas of the south of Scotland the forest consists of Pinus sylvestris, with the 

 exception of some parts of Tweedsmuir, where Betula alba replaces pine. As soon 

 as the Highland areas are entered the Upper Forest divides into two distinct zones 

 separated by 1-3 feet of peat in which no wood is found. In the Spey-Findhorn, 

 Findhorn-Nairn, Coire Bog districts, the peat between the upper and lower layers of 

 this forest is formed from Sphagnum, but in areas examined in the Grampians and in 

 Assynt, Betula nana and Salix Arbuscula are abundant between the two layers of 

 forest remains. The presence of these plants in some districts, and of Sphagnum beds 

 in others, between two layers of well-developed pine forest, is significant, and points to 

 a decided break in forest conditions at this time. This phenomenon is too widespread 

 to be due to local causes, for it is a constant feature in all the Highland areas 

 examined. 



Betula alba replaces Pinus sylvestris in the lower zone of the Upper Forest on the 



Grampians, in Assynt, and over much of the Caithness-Sutherland border ; in other 



words, at high elevations and in the extreme north. 



It is remarkable that until the Upper Forest is reached no extensive beds of Calluna 

 TRANS. ROY. SOC. EDIN., VOL. XLVI. PART I. (NO. 2). 9 



